The present invention is generally directed to carriers, and more specifically coated carriers and wherein the coating is generated by latex processes, and yet more specifically, by aggregation and coalescence or fusion of the latexes generated, and which latex is comprised of a core and a shell thereover, that is, for example, a structured latex. The resulting coated carriers can be selected for known electrophotographic imaging and printing processes, including digital color processes, and more specifically for imaging processes, especially xerographic processes, with high toner transfer efficiency, such as those obtained with a compact machine design without a cleaning component, or those that are designed to provide high quality colored images with excellent image resolution, acceptable signal-to-noise ratio, and image uniformity, and for imaging systems wherein excellent carrier triboelectric charging values and carriers with tuneability or preselected triboelectric charge are generated.
Aspects of the present invention relate to coated carrier particles and wherein the coating is comprised of a latex polymer with a core-shell structure, or a core encapsulated within a shell polymer or shell coating, and which structure possesses, for example, excellent fix and excellent gloss characteristics and wherein the structure can be generated by, for example, semicontinuous methods, emulsion polymerization, consecutive emulsion polymerization sequences and the like. The latexes of core and shell which can be prepared by a single stage reaction are more specifically of a unimodal molecular weight distribution and single glass transition temperature. A wide variety of latex polymers of for example, differing homopolymeric and copolymeric composition, such as styrene-butadiene-acrylic acid copolymers, styrene-butyl acrylate-acrylic acid copolymers, acrylic homopolymers and copolymers which possess specific chemical, mechanical and/or triboelectrical properties for toner and carrier applications can be generated. With the core-shell latexes one can select the optimum properties of each of the core and shell resins, or polymers, such as gloss and fix, which otherwise may not readily obtainable by a single latex. Another advantage of the structured latexes is that the gloss and fix levels can be varied, within for example, the limits of individual polymer properties by adjusting the glass transition temperature, molecular weight, or proportions of each polymer of the core and of the shell. Also, when resin A, the carrier core polymer, possesses a low molecular weight of about 5,000 to about 25,000 there could result for the developed image, an image gloss of greater than 50 gloss units, however, the fix may be poor, wherein the MFT is higher than 190xc2x0 C., or from about 195xc2x0 C. to about 225xc2x0 C., while if resin B has a high molecular weight of about 40,000 to about 80,000, there could result a poor gloss of, for example, an image gloss lower than about 50 gloss units, or from about 30 to about 45 gloss units, and wherein the MFT minimum toner fixing temperature is lower than about 180xc2x0 C., or from about 150xc2x0 C. to about 175xc2x0 C. By combining the above resins into a core-shell latex, there can be obtained excellent fix and acceptable gloss.
The advantages thereof of the carriers of the present invention include in embodiments high robust carrier tribo charge of a positive value, high toner tribo charge of a negative value, excellent admix, for example from about 1 to about 30 seconds as determined in the charge spectrograph, and the like; more specifically, the toner tribo can be, for example, from about a minus 50 to about a minus 150, from about a minus 55 to about a minus 90, or from about a minus 60 to about a minus 85, with corresponding positive tribo charges for the carrier; increased resistance of the carrier to mechanical aging in a xerographic environment and a decreased sensitivity of the carrier triboelectric value to the relative humidity of the environment. The tribo can be determined by a number of known methods, such as the use of a Faraday Cage. With respect to high toner tribo charge of a negative value, this property is of interest for xerographic, especially color applications, primarily because there is enabled development of toner particles into regions of the imaging member, such as a photoreceptor where strong fringe electrical fields exist, that is, at the borders of solids areas and lines. Developing toner particles through these fringe fields minimizes or eliminates the untoned part of the image which appears between two adjacent colors in an image.
A number of coated carriers have been disclosed, reference for example the patents recited hereinbefore and also, for example, U.S. Pat. No. 3,590,000. Emulsion/aggregation/coalescence processes for the preparation of toners are illustrated in a number of Xerox patents, the disclosures of each of which are totally incorporated herein by reference, such as U.S. Pat. No. 5,290,654, U.S. Pat. No. 5,278,020, U.S. Pat. No. 5,308,734, U.S. Pat. No. 5,370,963, U.S. Pat. No. 5,344,738, U.S. Pat. No. 5,403,693, U.S. Pat. No. 5,418,108, U.S. Pat. No. 5,364,729, and U.S. Pat. No. 5,346,797; and also of interest may be U.S. Pat. Nos. 5,348,832; 5,405,726; 5,366,841; 5,496,676; 5,527,658; 5,585,215; 5,650,255; 5,650,256 and 5,501,935 (spherical toners). The appropriate components and processes of the above Xerox patents can be selected for the present invention in embodiments thereof.
It is a feature of the present invention to provide coated carriers and developers thereof containing toner with many of the advantages illustrated herein and more specifically wherein high stable carrier turboelectric charging is achievable.
More specifically, a feature of the present invention relates to the preparation of coated carrier particles and wherein the coating is generated from latexes, especially latex particles having a core/shell morphology by a semicontinuous, consecutive emulsion polymerization in sequence with different monomers and wherein the second stage monomer is polymerized in the presence of seed latex particles, and which seed particles can be prepared separately, or formed in situ and wherein control latexes with appropriate Mns, Mws, and Tgs whereby the core polymer gloss and the shell polymer controls fix.
In another feature of the present invention there are provided simple and economical processes for the preparation of coated carrier particles and which coating is prepared from latexes of a core and a shell thereover and wherein the extent of carrier turboelectric charging can be varied and preselected by the regions in which electropositive components such as amino methacrylate polymers are dispersed in the coating surface, and wherein high viscosity carrier cores of a high electropositive charge undergo film formation based primarily on the increased flow characteristics of the shell.
In a further feature of the present invention there is provided a process for the preparation of carrier particles by aggregation and coalescence, or fusion (aggregation/coalescence) of a structured latex and a carrier core.